Piezoelectric element, liquid ejecting head, and liquid ejecting apparatus

ABSTRACT

A piezoelectric element comprises a piezoelectric layer consisting of a complex oxide having a perovskite structure containing bismuth and iron and electrodes provided to the piezoelectric layer. The complex oxide further contains a first dopant element that is at least one selected from the group consisting of sodium, potassium, calcium, strontium and barium, and a second dopant element that is cerium.

CROSS-REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2011-009282,filed Jan. 19, 2011 is expressly incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a liquid ejecting head and a liquidejecting apparatus, each including a pressure generating chambercommunicating with a nozzle aperture and a piezoelectric element thatincludes a piezoelectric layer and electrodes applying a voltage to thepiezoelectric layer and functions to change the pressure in the pressuregenerating chamber, and relates to the piezoelectric element.

2. Related Art

Some piezoelectric actuators used in liquid ejecting heads include apiezoelectric element having a structure in which a piezoelectric layermade of a piezoelectric material capable of electromechanicalconversion, such as a crystallized dielectric material, is disposedbetween two electrodes. Ink jet recording heads are a typical type ofliquid ejecting head. An ink jet recording head includes a vibrationplate defining a part of a pressure generating chamber communicatingwith nozzle apertures through which ink droplets are ejected. In the inkjet recording head, a piezoelectric element deforms the vibration plateto apply a pressure to the ink in the pressure generating chamber,thereby ejecting ink droplets through the nozzle apertures.

The piezoelectric material (piezoelectric ceramic) used for forming thepiezoelectric layer of such a piezoelectric element is required to havehigh piezoelectric properties, and a typical example of thepiezoelectric material is lead zirconate titanate (PZT)(JP-A-2001-223404).

On the other hand, it is desirable to reduce lead from piezoelectricmaterials, from the viewpoint of environmental protection. An exemplarylead-free piezoelectric material is BiFeO₃, which has a perovskitestructure expressed by ABO₃. In the ABO₃ structure, A represents the Asite and has 12 oxygen ligands, and B represents the B site and has 6oxygen ligands. However, for example, BiFeO₃-based piezoelectricmaterials are less insulating and liable to cause leakage current. Ifleakage current is liable to occur, the material is likely to crack whenit is used while a high voltage is applied, and is therefore difficultto use in a liquid ejecting head. Accordingly, piezoelectric materialsused in piezoelectric elements are required to have a high insulationvalue of 1×10⁻³ A/cm² or less in use, for example, at a typical drivingvoltage of 25 V.

This issue arises not only in ink jet recording heads, but also in otherliquid ejecting heads that eject droplets other than ink, andpiezoelectric elements used for applications other than liquid ejectingheads have the same issue. Furthermore, leakage current results in aserious problem that the energy consumption of the piezoelectric elementis increased when the piezoelectric element is used as a sensor. It isdesirable that leakage current be low as well in piezoelectric elementsused for piezoelectric sensors, infrared sensors, thermal sensors andpyroelectric sensors that are used at an applied voltage of, forexample, 1 V or less.

SUMMARY

An advantage of some aspects of the invention is that it provides aliquid ejecting head, a liquid ejecting apparatus and a piezoelectricelement whose environmental load is reduced, and whose insulation valueis increased to suppress leakage current.

According to an aspect of the invention, a liquid ejecting head isprovided which includes a pressure generating chamber communicating witha nozzle aperture and a piezoelectric element. The piezoelectric elementincludes a piezoelectric layer and electrodes disposed on thepiezoelectric layer. The piezoelectric layer is made of a complex oxidehaving a perovskite structure including an A site and a B site andcontaining bismuth and iron. The complex oxide contains a first dopantelement and a second dopant element. The first dopant element is atleast one selected from the groups consisting of sodium, potassium,calcium, strontium and barium, and the second dopant element is cerium.

This structure can suppress the occurrence of leakage current andachieve a piezoelectric element that can exhibit a high insulationvalue, and, thus, the liquid ejecting head can exhibit high durability.In addition, since the piezoelectric material does not contain lead, theenvironmental load of the piezoelectric element can be reduced.

Preferably, the A site contains bismuth, the first dopant element andthe second dopant element, and the B site contains iron.

In this instance, the A site may have a defect, and the B site containsbismuth.

Preferably, the complex oxide further contains barium titanate. Thus,the liquid ejecting head has a piezoelectric element exhibiting a stillhigher piezoelectric property (strain).

According to another aspect of the invention, a liquid ejectingapparatus including the above-described liquid ejecting head isprovided.

The liquid ejecting apparatus includes the highly insulatingpiezoelectric element in which leakage current can be suppressed, andthus exhibits high durability. In addition, since the piezoelectricmaterial does not contain lead, the environmental load of the liquidejecting apparatus can be reduced.

According to still another aspect of the invention, a piezoelectricelement is provided which includes a piezoelectric layer made of acomplex oxide and electrodes disposed on the piezoelectric layer. Thecomplex oxide has a perovskite structure containing bismuth and iron,and contains a first dopant element and a second dopant element. Thefirst dopant element is at least one selected from the group consistingof sodium, potassium, calcium, strontium and barium, and the seconddopant element is cerium.

This structure can suppress leakage current and achieve a piezoelectricelement that can exhibit a high insulation value. In addition, since thepiezoelectric material does not contain lead, the environmental load ofthe piezoelectric element can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic exploded perspective view of a recording headaccording to an embodiment of the invention.

FIG. 2 is a plan view of the recording head according to the embodiment.

FIG. 3 is a sectional view of the recording head according to theembodiment.

FIG. 4 is a representation of the electronic density of states of BiFeO₃perfect crystal.

FIG. 5 is a representation of the electronic density of states of BiFeO₃in which Bi is 12.5% defective in the A site.

FIG. 6 is a representation of the electronic density of states of BiFeO₃in which Bi is substituted for 12.5% of Fe in the B site.

FIG. 7 is a representation of the electronic density of states ofPbZrTiO₃ in which Pb is substituted for 12.5% of transition metals inthe B site.

FIG. 8 is a representation of the electronic density of states of BiFeO₃in which 4% of oxygen in the oxygen site has been lost.

FIG. 9 is a schematic representation of the hopping conduction in acomplex oxide crystal.

FIG. 10 is a schematic representation of the hopping conduction in thecrystal of a complex oxide used in an embodiment of the invention.

FIG. 11 is a representation of the electronic density of states ofBiFeO₃ in which Na has been substituted for 12.5% of Bi in the A site.

FIG. 12 is a representation of the electronic density of states ofBiFeO₃ in which K has been substituted for 12.5% of Bi in the A site.

FIG. 13 is a representation of the electronic density of states ofBiFeO₃ in which Ca has been substituted for 12.5% of Bi in the A site.

FIG. 14 is a representation of the electronic density of states ofBiFeO₃ in which Sr has been substituted for 12.5% of Bi in the A site.

FIG. 15 is a representation of the electronic density of states ofBiFeO₃ in which Ba has been substituted for 12.5% of Bi in the A site.

FIG. 16 is a representation of the electronic density of states ofBiFeO₃ in which Ce has been substituted for 12.5% of Bi in the A site.

FIGS. 17A and 17B are sectional views showing a manufacturing process ofa recording head according to an embodiment of the invention.

FIGS. 18A to 18C are sectional views showing the manufacturing processof the recording head.

FIGS. 19A and 19B are sectional views showing the manufacturing processof the recording head.

FIGS. 20A to 20C are sectional views showing the manufacturing processof the recording head.

FIGS. 21A and 21B are sectional views showing the manufacturing processof the recording head.

FIG. 22 is a schematic view of a recording apparatus according to anembodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a schematic exploded perspective view of an ink jet recordinghead I, which is a type of liquid ejecting head, according to anembodiment of the invention. FIG. 2 is a plan view of the ink jetrecording head I shown in FIG. 1. FIG. 3 is a sectional view taken alongline III-III shown in FIG. 2. A flow channel substrate 10 is made ofmonocrystalline silicon, and a silicon dioxide elastic film 50 isdisposed on one surface of the flow channel substrate 10, as shown inFIGS. 1 to 3.

The flow channel substrate 10 has a plurality of pressure generatingchambers 12 arranged in parallel in the direction of their widths. Theflow channel substrate 10 also has a communicating section 13 thereinlocated outside the pressure generating chambers 12 in theirlongitudinal direction. The communicating section 13 communicates withthe pressure generating chambers 12 through corresponding ink supplychannels 14 and communication paths 15. The communicating section 13communicates with a manifold section 31 formed in a protective substrate(described later) to define a part of a manifold acting as a common inkchamber of the pressure generating chambers 12. Each ink supply channel14 has a smaller width than the pressure generating chamber 12, so thatthe flow channel resistance of the ink delivered to the pressuregenerating chamber 12 from the communicating section 13 is keptconstant. Although the ink supply channels 14 are formed by narrowingthe flow channels from one side in the present embodiment, the flowchannels may be narrowed from both sides in another embodiment.Alternatively, the ink supply channels 14 may be formed by reducing thedepth of the flow channels, instead of narrowing the flow channels. Inthe present embodiment, the flow channel substrate 10 has liquid flowchannels including the pressure generating chambers 12, thecommunicating section 13, the ink supply channels 14 and thecommunication paths 15.

The flow channel substrate 10 is joined to a nozzle plate 20 at the openside thereof with an adhesive, a thermal fusion film or the like. Thenozzle plate 20 has nozzle apertures 21 communicating with the endportions of the corresponding pressure generating chambers 12 on theopposite side to the ink supply channels 14. The nozzle plate 20 can bemade of, for example, glass-ceramic, monocrystalline silicon orstainless steel.

On the opposite side to the open side of the flow channel substrate 10,the above-mentioned elastic film 50 is disposed, and an adhesion layer56 having a thickness of, for example, about 30 to 50 nm and made oftitanium oxide or the like is disposed on the elastic film 50 to enhancethe adhesion between the elastic film 50 and the overlying firstelectrode 60. The elastic film 50 may be provided thereon with aninsulating film made of zirconium oxide or the like, if necessary.

Furthermore, piezoelectric elements 300 are disposed on the adhesionlayer 56. Each piezoelectric element 300 has a multilayer structureincluding a first electrode 60, a piezoelectric layer 70 having a smallthickness of 2 μm or less, preferably 0.3 to 1.5 μm, and a secondelectrode 80. The piezoelectric element 300 mentioned herein refers tothe portion including the first electrode 60, the piezoelectric layer 70and the second electrode 80. In general, either electrode of thepiezoelectric element 300 acts as a common electrode, and the otherelectrode and the piezoelectric layer 70 are formed for each pressuregenerating chamber 12 by patterning. Although in the present embodiment,the first electrode 60 acts as the common electrode of the piezoelectricelements 300 and the second electrode 80 is provided as discreteelectrodes of the piezoelectric elements 300, the functions of the firstand second electrodes may be reversed for the sake of convenience of thedriving circuit and wiring. An actuator device mentioned herein isdefined by a combination of the piezoelectric element 300 and avibration plate that can be displaced by the operation of thepiezoelectric element 300. Although in the embodiment above, the elasticfilm 50, the adhesion layer 56, the first electrode 60 and, optionally,an insulating film act as a vibration plate, the structure of thevibration plate is not limited to the above, and the elastic film 50 andthe adhesion layer 56 may not be provided. The piezoelectric element 300may double as a vibration plate in substance.

In the following description, the perovskite structure of complex oxidescontaining transition metals will be expressed by ABO₃. In theexpression, A represents the A site and has 12 oxygen ligands, and Brepresents the B site and has 6 oxygen ligands.

In the present embodiment, the piezoelectric layer 70 is made of acomplex oxide that has a perovskite structure containing bismuth (Bi)and iron (Fe), and contains at least one first dopant element selectedfrom the group consisting of sodium (Na), potassium (K), calcium (Ca),strontium (Sr) and barium (Ba) and a second dopant element that iscerium (Ce). Thus, leakage current can be suppressed, and consequently,the piezoelectric element can exhibit a high insulation value, as willbe described later. In addition, since the piezoelectric material doesnot contain lead, the environmental load of the piezoelectric elementcan be reduced.

In the perovskite structure of the complex oxide, the A site contains Biand the B site contains Fe. The Bi in the A site and the Fe in the Bsite may each be partially substituted with other elements. Exemplarysubstitution elements for the A site include lanthanum (La),praseodymium (Pr), neodymium (Nd), samarium (Sm), and yttrium (Y), andexemplary substitution elements for the B site include cobalt (Co),chromium (Cr), manganese (Mn), nickel (Ni), and copper (Cu).

The Bi of BiFeO₃ or the like is easily evaporated in manufacturingprocesses, particularly during firing of the piezoelectric layer.Consequently, a crystal defect is liable to occur in the A site. The Biremoved from the A site will diffuse into the atmosphere of themanufacturing chamber and to the lower electrode side. As Bi escapesfrom the system, oxygen is lost to maintain the balance of the number ofelectrons. The ratio of bismuth defects to oxygen defects is 2:3 fromthe viewpoint of the charge neutrality principle. Oxygen defects reducethe orbital energy of the d electrons of the transition metals throughCoulomb potential and narrow the band gap of the piezoelectric element.Thus, the presence of oxygen defects can be a direct cause of leakagecurrent. In order to reduce the number of oxygen defects, Bi defects canbe reduced. For this purpose, Bi may be added excessively to thestoichiometric composition in advance. However, an excessive amount ofBi enters not only the A site, but also the B site unintentionally in acertain proportion. The Bi having entered the B site acts as a supplysource of electron carriers, and leakage current thus occurs in thepiezoelectric element. It is therefore not suitable to add Biexcessively to the stoichiometric composition in a BiFeO₃ system.

As with Bi, lead (Pb) in conventionally used lead zirconate titanate(PbZrTiO₃, PZT) easily evaporates in manufacturing processes.Accordingly, in general, Pb is added excessively to the stoichiometriccomposition in advance. When Pb is excessive, Pb will unintentionallyenter the B site. However, the electronic structure of PZT can maintainthe band gap even if Pb has been unintentionally introduced to the Bsite, as will be described with reference to FIG. 7. Therefore, forproducing a piezoelectric material PbZrTiO₃, the insulation value of thePbZrTiO₃ is not reduced even if Pb is excessively added to thestoichiometric composition.

The present inventors have learned the following through examinationsusing first-principles electronic state calculation.

FIGS. 4 to 8 show electronic densities of states obtained byfirst-principles electronic state calculation. In these figures, thehorizontal axis represents the electronic energy difference (eV), andthe vertical axis represents the electronic density of states (DOS). Thepositive values of the DOS correspond to spin up components, and thenegative values of the DOS correspond to spin down components. For thefirst-principles electronic states calculation, an ultra softpseudopotential is used on the basis of the density functional methodwithin generalized gradient approximation (GGA). In order to takeaccount of the strong correlation effect resulting from the locality ofthe d electron orbitals, the GGA plus U method was used for thetransition metal atoms of the B site. Cutoff values of wave functionsand charge density are 20 hartrees and 360 hartrees, respectively. Thesuper cell of the crystal used for calculation was formed with 8 (2×2×2)ABO₃-form perovskite structures. The k-point mesh (mesh of reciprocallattice points) is 4×4×4.

FIG. 4 shows the electronic density of states of the perfect crystal ofbismuth ferrate (BiFeO₃). FIG. 5 shows the electronic density of statesof BiFeO₃ in which Bi in the A site is 12.5% defective. FIG. 6 shows theelectronic density of states of BiFeO₃ whose B site is substituted with12.5% of Bi. FIG. 7 shows the electronic density of states of leadzirconate titanate (PbZrTiO₃) whose B site is substituted with 12.5% ofPb. FIG. 8 shows the electronic density of states of bismuth ferrate(BiFeO₃) in which 4% of oxygen in the oxygen site has been lost.

In all cases shown in FIGS. 4, 5, 6 and 8, the complex oxide was stablein the antiferromagnetic state.

As shown in FIG. 4, in BiFeO₃ perfect crystal, that is, in the casewhere each site has no vacancies and where Bi has not been substitutedwith any other element, the highest electron-occupied level (Ef) lies atthe top of the valance band and the band gap is widened. The material isthus insulating. In FIG. 4, the valence band is on the low energy sideof the band gap and the conduction band is on the high energy side ofthe band gap.

The highest electron-occupied level refers to the highest energy levelof orbitals that electrons occupy in electronic energy obtained by anelectron state simulation. In each graph, the highest electron-occupiedlevel (Ef) lies at the zero point on the horizontal axis.

As shown in FIG. 5, when part of the Bi in the A site of BiFeO₃ is lost,thereby producing a defect, empty states appear on the positive side ofthe position at an energy of 0 eV. In other words, the highestelectron-occupied level enters the energy region of valence band. Thisshows that the system has become non-insulating and produced holecarries, thus exhibiting p type conductivity. By measuring the emptyarea of the density of states, it can be shown that the loss of Bi inthe A site provides three hole carriers.

When the B site contains bismuth (Bi), occupied states appear on thenegative side of the position at an energy of 0 eV, as shown in FIG. 6.In other words, the highest electron-occupied level enters the energyregion of the conduction band. This shows that the system has becomenon-insulating and produced electron carriers, thus exhibiting n-typeconductivity. By measuring the area with the density of occupied states,it can be shown that the Bi of the B site provides two electroncarriers. It is therefore undesirable that an excessive amount of Bi isused in a composition prepared in the manufacturing process from theviewpoint of suppressing leaking. Such an amount of Bi results inintroduction of electron carriers to the system.

FIG. 7 shows the electronic density of states of PZT whose B sitecontains Pb. PZT-based piezoelectric materials can maintain the band gapin the electronic structure, as shown in FIG. 7, even if the B sitecontains unintended Pb. Accordingly, for producing a PbZrTiO₃piezoelectric material, the insulation value of the piezoelectricmaterial is not reduced even if Pb has been excessively added to thestoichiometric composition.

When 4% of oxygen has been lost from the oxygen site of BiFeO₃, occupiedstates appear on the negative side of the position at an energy of 0 eV,as shown in FIG. 8. In other words, the highest electron-occupied levelenters the energy region of the conduction band. This shows that thesystem has become non-insulating and produced electron carriers, thusexhibiting n-type conductivity. By measuring the area of the density ofoccupied states, it can be shown that the loss in the oxygen siteprovides two electron carriers.

Thus, BiFeO₃ has both an n-type defect and a p-type defect, as shown inFIGS. 5, 6 and 8. In a semiconductor material, for example, theelectronic states of carriers in the conduction band and the valenceband are of free electrons. Accordingly, hole carriers deriving from thep-type defect and electron carriers deriving from the n-type defectspread spatially, thus canceling each other out. On the other hand, in atransition metal oxide, carriers in the conduction band and the valenceband are localized and their mobilities are small. Consequently, holecarriers and electron carriers do not completely cancel each other out.Thus, in the transition metal oxide, carriers that are not canceled outcontribute to electric conduction of the system as hopping conduction.

FIG. 9 schematically shows the state of the hopping conduction of atransition metal compound having p-type defects and n-type defects. Inthe transition metal compound, channels for hopping conduction areformed through which hole carriers and electron carriers transfer viathe p-type defects and the n-type defects, respectively. In this state,even if the transition metal compound is doped so as to compensate forcarriers of one type, hopping conduction caused by the other type cannotbe suppressed. This is probably the reason why the insulation value ofBiFeO₃ cannot be increased.

Accordingly, leakage current cannot be prevented even if an n-typedopant element that can eliminate the p-type defect or a p-type dopantelement that can eliminate the n-type defect is independentlyintroduced. However, by simultaneously introducing an n-type dopantelement and a p-type dopant element (co-doping), leakage current causedby the p-type defect and leakage current caused by the n-type defect canbe prevented.

The invention is based on the above-described findings, and in theinvention, a transition metal complex oxide, such as BiFeO₃, issimultaneously doped (co-doped) with an n-type dopant element and ap-type dopant element so as to prevent leakage current caused by thep-type defect and leakage current caused by the n-type defect and thusto enhance the insulation value of the complex oxide.

FIG. 10 schematically shows a transition metal compound used in anembodiment of the invention that has been co-doped with an n-type dopantelement and a p-type dopant element. By co-doping a transition metalcomplex oxide, such as BiFeO₃, with an n-type dopant element and ap-type dopant element, the p-type defect is canceled out by the n-typedopant element, and the n-type defect is canceled out by the p-typedopant element. Thus, both the leakage current generated by hoppingamong the p-type defects and the leakage current generated by hoppingamong the n-type defects can be significantly reduced.

More specifically, in the present embodiment, for example, BiFeO₃ isdoped with at least one first dopant element selected from the groupsconsisting of sodium (Na), potassium (K), calcium (Ca), strontium (Sr)and barium (Ba) and with a second dopant element that is cerium (Ce).

The first and second dopant elements are substituted for elements of theA site. The first dopant element acts as a p-type donor and cancels outn-type defects, and the second dopant element acts as an n-type donorand cancels out p-type defects.

FIGS. 11 to 16 show electronic densities of states of BiFeO₃-basedcrystals in which 12.5% of Bi of the A site has been substituted withsodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba)and cerium (Ce), respectively. The electronic density of states in eachfigure was obtained by the first-principles electronic statecalculation. The first-principles electronic state calculation wasperformed under the same conditions as mentioned above.

As shown in FIGS. 11 and 15, empty states appears on the positive sideof the position at an energy of 0 eV by forcibly substituting part ofthe Bi of BiFeO₃ with any one of the first dopant elements: sodium (Na),potassium (K), calcium (Ca), strontium (Sr) and barium (Ba). In otherwords, the highest electron-occupied level enters the energy region ofvalence band. This shows that the system has become non-insulating andproduced hole carriers, and thus exhibiting p-type conductivity. Bymeasuring the area of the density of empty states, it can be shown thatthe first dopant element for the A site provides hole carriers.Specifically, when the first dopant element is Na or K, two holecarriers are provided. Also, when the first dopant element is Ca, Sr, orBa, one hole carrier is provided. Thus, it has been shown that each ofsodium (Na), potassium (K), calcium (Ca), strontium (Sr) and barium (Ba)acts as a p-type donor.

On the other hand, when part of the Bi of BiFeO₃ is forcibly substitutedwith the second dopant element Ce, occupied states appear on thenegative side of the position of an energy of 0 eV, as shown in FIG. 16.In other words, the highest electron-occupied level enters the energyregion of the conduction band. This shows that the system has becomenon-insulating and produced electron carriers, thus exhibiting n-typeconductivity. By measuring the area of the density of occupied states,it can be shown that the Ce having been substituted at the A siteprovides one electron carrier. This shows that cerium acts as an n-typedonor.

As described above, in the present embodiment, BiFeO₃ is doped with atleast one first dopant element selected from the group consisting of Na,K, Ca, Sr and Ba to cancel out n-type defects, and it is also doped withCe as a second dopant element to cancel out p-type defects.Consequently, high insulation value can be maintained.

Since Na and K used as the first dopant element each give two holecarriers to a system, they can each cancel out two electron carriersproduced from an n-type defect. Also, since Ca, Sr and Ba used as thefirst dopant element each give one hole carrier to a system, they caneach cancel out one electron carrier produced from an n-type defect.

Also, since the second dopant element Ce gives one electron carrier to asystem, it can cancel out one hole carrier produced from a p-typedefect.

These first and second dopant elements located in the A site do notalways completely eliminate Bi defects. Hence, the atomic defect in theA site can be present together with the first and second dopant elementsof the A site. For example, even if Bi defects are present in the Asite, the dopant elements do not always enter the positions from whichBi atoms have been lost, and the dopant elements may be introduced bybeing substituted for other bismuth atoms in the A site. The dopantelements then act so as to cancel out the bismuth (n type) of the B siteand the bismuth defects (p type) of the A site.

Preferably, the first dopant element, which is at least one selectedfrom the group consisting of Na, K, Ca, Sr and Ba, is introduced in anamount equivalent to the amount of expected n-type defects, and thesecond dopant element Ce is introduced in an amount equivalent to theamount of expected p-type defects. For example, the proper amounts ofthese dopant elements are 10% or less, and preferably 5% or less. Thefirst dopant elements may be introduced singly, or in combination at onetime.

These dopant elements, which differ from the elements constituting theperovskite structure of the original material, are introduced accordingto the amount of defects in the crystal.

In the present embodiment, the A site of the complex oxide may containlanthanum having a large ionic radius. The presence of lanthanum cansuppress the formation of other phases different from the perovskitestructure. The ability of lanthanum to form a covalent bond with theclosest oxygen is much lower than that of bismuth. Accordingly, thepotential barrier of lanthanum lowers against the rotation ofpolarization moments by an applied electric field. Conditions underwhich the rotation of polarization moments is likely to occur easilyenhance the piezoelectric properties. Also, since lanthanum is a metalhaving an ionic valence of +3, the valence balance of the system in thepresent embodiment does not change and does not have an adverse effecton the conditions of leakage current even if lanthanum is present in theA site. Preferably, the proportion on a mole basis of lanthanum in the Asite is in the range of 0.05 to 0.20 relative to the total of bismuthand lanthanum. Praseodymium, neodymium and samarium are each an elementhaving a large radius and having an ionic valence of +3, and thereforehave the same effect as lanthanum.

The complex oxide may contain cobalt (Co) or chromium (Cr) or both inthe B site, in addition to Fe. These elements are preferably containedin the range of 0.125 to 0.875 on a mole basis relative to the total ofall elements in the B site. Thus, when the complex oxide contains Fe, Coand Cr in predetermined proportions, the insulation value and magnetismof the complex oxide can be maintained. In addition, such a complexoxide has a morphotropic phase boundary (MPB), and therefor exhibitshigh piezoelectric properties. In particular, when the molar ratio of Coor Cr to the total of Fe and Co or Cr is about 0.5, the piezoelectricconstant is increased due to the MPB, and, thus, the piezoelectricproperties can be enhanced.

Furthermore, the complex oxide preferably contains barium titanatehaving a stoichiometric composition (for example, BaTiO₃ having aperovskite structure), in addition to BiFeO₃. In this instance, a MPBappears between BiFeO₃ having a rhombohedral structure and BaTiO₃ havinga tetragonal structure at room temperature. The composition ratio inwhich a MPB appears is BiFeO₃:BaTiO₃=3:1. In this composition, thepiezoelectric layer 70 can exhibit high piezoelectric properties, and,consequently, can displace the vibration plate significantly at a lowvoltage. If the piezoelectric layer 70 contains barium titanate, thepiezoelectric material is a complex oxide (for example, (Bi, Ba) (Fe,Ti)O₃) having a perovskite structure containing barium titanate and amain constituent, for example, bismuth ferrate, and simultaneously dopedwith the first dopant element and the second dopant element. Inparticular, if barium is used as the first dopant element, barium isfurther added to stoichiometric barium titanate (BaTiO₃).

In the present embodiment, the piezoelectric layer 70 has a monocliniccrystal structure. Hence, the piezoelectric layer 70 made of a complexoxide having a perovskite structure has monoclinic symmetry. Such apiezoelectric layer 70 can exhibit high piezoelectric properties. Thisis probably because the polarization moments of the piezoelectric layer70 have a structure easy to rotate under an electric field applied inthe direction perpendicular to the surface. In the piezoelectric layer70, the variation in polarization moment and the deformation of thecrystal structure are directly combined, and this determines thepiezoelectric properties. Thus, structures in which polarization momentseasily change can exhibit high piezoelectric properties.

Furthermore, the piezoelectric layer 70 preferably has an engineereddomain structure in which the polarization leans at a predeterminedangle (50 to 60 degrees) with the direction perpendicular to the surfaceof the layer.

The crystalline orientation of the piezoelectric layer 70 may be in the(100), (111) or (110) plane or in mixed directions, as long assatisfying the requirements of polarization direction in the aboveengineered domain.

The second electrode 80 provided for each piezoelectric element 300 isconnected with a lead electrode 90 made of, for example, gold (Au)extending from one end to the ink supply channel 14 side of the secondelectrode 80 to the upper surface of the elastic film 50 and,optionally, the upper surface of an insulating film.

A protective substrate 30 having a manifold section 31 defining at leastpart of a manifold 100 is joined to the flow channel substrate 10 havingthe piezoelectric elements 300 with an adhesive 35 so as to cover thefirst electrode 60, the elastic film 50, an optionally providedinsulating film, and the lead electrodes 90. The manifold section 31passes through the thickness of the protective substrate 30 and extendsalong the widths of the pressure generating chambers 12. Thus, themanifold section 31 communicates with the communicating section 13 ofthe flow channel substrate 10 to form the manifold 100 acting as thecommon ink chamber of the pressure generating chambers 12. Thecommunicating section 13 of the flow channel substrate 10 may be dividedfor each pressure generating chamber 12, and only the manifold section31 may serve as the manifold. Alternatively, the flow channel substrate10 may have only the pressure generating chambers 12, and the manifold100 and ink supply channels 14 communicating with the respectivepressure generating chambers 12 are formed in a member between the flowchannel substrate 10 and the protective substrate 30, such as theelastic film 50 and an optionally provided insulating film.

A piezoelectric element-protecting section 32 is formed in the region ofthe protective substrate 30 corresponding to the piezoelectric elements300. The Piezoelectric element-protecting section 32 has a space so thatthe piezoelectric elements 300 can operate without interference. Thespace of the piezoelectric element-protecting section 32 is intended toensure the operation of the piezoelectric elements 300, and may or maynot be sealed.

Preferably, the protective substrate 30 is made of a material havingsubstantially the same thermal expansion coefficient as the flow channelsubstrate 10, such as glass or ceramic. In the present embodiment, theprotective substrate 30 is made of the same monocrystalline silicon asthe flow channel substrate 10.

The protective substrate 30 has a through hole 33 passing through thethickness of the protective substrate 30. The ends of the leadelectrodes 90 extending from the piezoelectric elements 300 are exposedin the through hole 33.

A driving circuit 120 is secured on the protective substrate 30 anddrives the piezoelectric elements 300 arranged in parallel. The drivingcircuit 120 may be a circuit board, a semiconductor integrated circuit(IC) or the like. The driving circuit 120 is electrically connected toeach lead electrode 90 with a conductive connection wire 121, such asbonding wire.

Furthermore, a compliance substrate 40 including a sealing film 41 and afixing plate 42 is joined on the protective substrate 30. The sealingfilm 41 is made of a flexible material having a low rigidity, and sealsone end of the manifold section 31. The fixing plate 42 is made of arelatively hard material. The portion of the fixing plate 42 opposingthe manifold 100 is completely removed to form an opening 43; hence themanifold 100 is closed at one end only with the flexible sealing film41.

The ink jet recording head I of the present embodiment draws an inkthrough an ink inlet connected to an external ink supply unit (notshown). The ink is delivered to fill the spaces from the manifold 100 tothe nozzle apertures 21. Then, the ink jet recording head I applies avoltage between the first electrode 60 and each second electrode 80corresponding to the pressure generating chambers 12, according to therecording signal from the driving circuit 120. Thus, the elastic film50, the adhesion layer 56, the first electrode 60 and the piezoelectriclayers 70 are deformed to increase the internal pressure in the pressuregenerating chambers 12, thereby ejecting the ink through the nozzleapertures 21.

A method for manufacturing the ink jet recording head according to thepresent embodiment will be described with reference to FIGS. 17A to 21B.FIGS. 17A to 21B are sectional views of the pressure generating chambertaken in the longitudinal direction.

As shown in FIG. 17A, a silicon dioxide (SiO₂) film is formed for anelastic film 50 on the surface of a silicon wafer 110 for a flow channelsubstrate by thermal oxidation or the like. Then, an adhesion layer 56is formed of, for example, titanium oxide on the SiO₂ elastic film 50 bysputtering, thermal oxidation or the like, as shown in FIG. 17B.

Subsequently, as shown in FIG. 18A, a platinum film for a firstelectrode 60 is formed over the entire surface of the adhesion layer 56by sputtering or the like.

Then, a piezoelectric layer 70 is formed on the platinum film. Thepiezoelectric layer 70 may be formed by a chemical solution method suchas a sol-gel method or metal-organic decomposition (MOD), in which acoating of a solution containing a metal complex is dried and fired at ahigh temperature to form a metal oxide piezoelectric layer, or a gasphase method such as sputtering. Other methods may be applied forforming the piezoelectric layer 70, such as laser ablation, pulsed laserdeposition (PLD), CVD or aerosol deposition.

More specifically, the piezoelectric layer 70 is formed as follows.First, as shown in FIG. 18B, a sol or MOD solution (precursor solution)is applied onto the first electrode 60 by spin coating or the like, thusforming a piezoelectric precursor film 71 (coating).

The precursor solution is prepared by mixing metal complexes that canform a complex oxide containing Bi and Fe, optionally La, Co or Cr, andthe first and second dopant elements so that each metal can have adesired proportion on a mole basis, and by dissolving or dispersing themixture in an organic solvent, such as an alcohol.

In this process, the “metal complexes that can form a complex oxidecontaining Bi and Fe, optionally La, Co or Cr, and the first and seconddopant elements” refer to metal complexes in a mixture, each containingat least one metal of Bi, Fe, optionally added La, Co or Cr, and thefirst and second dopant elements. Examples of such metal complexesinclude metal alkoxides, organic acid salts, and β-diketone complexes.

The metal complex containing Bi may be bismuth 2-ethylhexanoate. Themetal complex containing Fe may be iron 2-ethylhexanoate. The metalcomplex containing Co may be cobalt 2-ethylhexanoate. The metal complexcontaining Cr may be chromium 2-ethylhexanoate. The metal complexcontaining La may be lanthanum 2-ethylhexanoate. Examples of the metalcomplexes containing Na include sodium 2-ethylhexanoate, sodium acetate,sodium acetylacetonate, and sodium tert-butoxide. Examples of the metalcomplexes containing K include potassium 2-ethylhexanoate, potassiumacetate, potassium acetylacetonate, and potassium tert-butoxide. Themetal complex containing Ca may be calcium 2-ethylhexanoate. The metalcomplex containing Sr may be strontium 2-ethylhexanoate. The metalcomplex containing Ba may be barium 2-ethylhexanoate. The metal complexcontaining Ce may be cerium 2-ethylhexanoate. Metal complexes containingtwo or more elements of Bi, Fe, Co and La may be used.

Subsequently, the piezoelectric precursor film 71 is heated to apredetermined temperature (150 to 400° C.) to be dried for a certaintime (drying). Then, the dried piezoelectric precursor film 71 isfurther heated to a predetermined temperature and allowed to stand for acertain time to be degreased (degreasing). The degreasing mentionedherein is performed to convert organic components in the piezoelectricprecursor film 71 into, for example, NO₂, CO₂ or H₂O and thus to removethe organic components. The drying and degreasing may be performed inany atmosphere without particular limitation, and may be performed inthe air or an inert gas atmosphere.

Then, as shown in FIG. 18C, the piezoelectric precursor film 71 isheated to a predetermined temperature, for example, to about 600 to 800°C., and allowed to stand for a certain time, thus being crystallized toform a piezoelectric film 72 (firing). This firing operation may beperformed in any atmosphere without particular limitation, and may beperformed in the air or an inert gas atmosphere.

The heating apparatus used for the drying, degreasing and firingoperations may be a rapid thermal annealing (RTA) apparatus using aninfrared lamp for heating, or a hot plate.

Then, a resist layer (not shown) having a predetermined shape is formedon the piezoelectric film 72, and the piezoelectric film 72 and thefirst electrode 60 are simultaneously patterned in such a manner thattheir sides are inclined, as shown in FIG. 19A, using the resist layeras a mask.

After removing the resist layer, the sequence of coating, drying anddegreasing, or the sequence of coating, drying, degreasing and firing isrepeated according to the desired thickness. Thus a piezoelectric layer70 having a desired thickness including a plurality of piezoelectricfilms 72 is formed, as shown in FIG. 19B. If, for example, a coatingformed by a single coating operation has a thickness of about 0.1 μm,the piezoelectric layer 70 including 10 piezoelectric films 72 has atotal thickness of about 1.1 μm. Although a plurality of piezoelectricfilms 72 are layered in the present embodiment, the piezoelectric layer70 may include only a single piezoelectric film 72 in anotherembodiment.

After the piezoelectric layer 70 is formed, a second electrode 80 isformed of platinum on the piezoelectric layer 70 by sputtering or thelike, as shown in FIG. 20A, and the piezoelectric layer 70 and thesecond electrode 80 are simultaneously patterned to form piezoelectricelements 300, each including the first electrode 60, the piezoelectriclayer 70 and the second electrode 80, in the regions corresponding tothe pressure generating chambers 12. The patterning of the piezoelectriclayer 70 and the second electrode 80 can be performed at one time by dryetching through a resist layer (not shown) having a predetermined shape.After this operation, post-annealing may be performed at a temperaturein the range of 600 to 800° C., if necessary. Thus, favorable interfacescan be formed between the piezoelectric layer 70 and the first electrode60 and between the piezoelectric layer 70 and the second electrode 80,and, in addition, the crystallinity of the piezoelectric layer 70 can beenhanced.

Then, as shown in FIG. 20B, a film is formed of, for example, gold (Au)over the entire surface of the flow channel substrate wafer 110, and ispatterned into lead electrodes 90 for each piezoelectric element 300through a mask pattern (not shown) made of, for example, resist.

Then, as shown in FIG. 20C, a silicon protective substrate wafer 130 fora plurality of protective substrates 30 is bonded to the piezoelectricelement 300 side of the flow channel substrate wafer 110 with anadhesive 35, and the thickness of the flow channel substrate wafer 110is reduced.

Turning to FIG. 21A, a mask layer is formed on the surface of the flowchannel substrate wafer 110 opposite to the protective substrate wafer130 and is patterned into a mask 52 having a predetermined shape.

Subsequently, as shown in FIG. 21B, the flow channel substrate wafer 110is subjected to anisotropic etching (wet etching) using an alkalinesolution, such as KOH, through the mask 52 to form the pressuregenerating chambers 12 corresponding to the piezoelectric elements 300,the communicating section 13, the ink supply channels 14 and thecommunication paths 15 therein.

Then, unnecessary outer portions of the flow channel substrate wafer 110and protective substrate wafer 130 are cut off by, for example, dicing.Subsequently, a nozzle plate 20 having nozzle apertures 21 therein isjoined to the surface of the flow channel substrate wafer 110 oppositethe protective substrate wafer 130 after the mask 52 has been removed,and a compliance substrate 40 is joined to the protective substratewafer 130. The flow channel substrate wafer 110 joined to othersubstrates together is cut into chips as shown in FIG. 1, each includinga flow channel substrate 10 and other members. Thus, the ink jetrecording head I of the present embodiment is produced.

Although an exemplary embodiment of the invention has been described,the invention is not limited to the disclosed embodiment. For example,in the above embodiment, a monocrystalline silicon substrate is used asthe flow channel substrate 10. However, the flow channel substrate 10may be made of, for example, silicon-on-insulator (SOI) or glass,without particular limitation.

Also, although the piezoelectric element 300 of the above embodimentincludes the first electrode 60, the piezoelectric layer 70 and thesecond electrode 80 that are stacked in that order on a substrate (flowchannel substrate 10), the structure of the piezoelectric element is notlimited to this structure. For example, an embodiment of the inventioncan be applied to a vertical vibration piezoelectric element includinglayers of a piezoelectric material and an electrode material alternatelyformed so as to expand and contract in the axis direction.

The ink jet recording head according to an embodiment of the inventioncan be installed in an ink jet recording apparatus to serve as a part ofa recording head unit including flow channels communicating with an inkcartridge or the like. FIG. 22 is a schematic perspective view of suchan ink jet recording apparatus II.

The ink jet recording apparatus shown in FIG. 22 includes recording headunits 1A and 1B each including the ink jet recording head I. Cartridges2A and 2B for supplying ink are mounted in the respective recoding headunits 1A and 1B. The recording head units 1A and 1B are loaded on acarriage 3 secured for movement along a carriage shaft 5 of an apparatusbody 4. The recording head units 1A and 1B eject, for example, a blackink composition and a color ink composition, respectively.

The carriage 3 on which the recording head units 1A and 1B are mountedis moved along the carriage shaft 5 by transmitting a driving force froma driving motor 6 to the carriage 3 through a plurality of gears (notshown) and a timing belt 7. In the apparatus body 4, a platen 8 isdisposed along the carriage shaft 5 so that a recording sheet S, whichis a print medium such as a paper sheet, fed from, for example, a feedroller (not shown), is transported over the platen 8.

Although the ink jet record head units 1A and 1B each have one ink jetrecording head I in the embodiment shown in FIG. 22, the ink jet recordhead unit 1A or 1B may have two or more ink jet recording heads withoutbeing limited to the above structure.

Although the above embodiment has described an ink jet recording head asthe liquid ejecting head, the invention is intended for any type ofliquid ejecting head, and may be applied to other liquid ejecting headsthat eject liquid other than ink. Other liquid ejecting heads includevarious types of recording head used in image recording apparatuses suchas printers, color material ejecting heads used for manufacturing colorfilters of liquid crystal displays or the like, electrode materialejecting heads used for forming electrodes of organic EL displays orfield emission displays (FEDs), and bioorganic material ejecting headsused for manufacturing bio-chips.

Since the piezoelectric element of the embodiments of the invention canexhibit a high insulation value and high piezoelectric properties, asdescribed above, it can be used in liquid ejecting heads represented byan ink jet recording head. However, the piezoelectric element can beused in other applications without particular limitation. For example,the piezoelectric element may be applied to ultrasonic devices such asultrasonic oscillators, ultrasonic motors, piezoelectric transformers,and various types of sensors, such as infrared sensors, ultrasonicsensors, thermal sensors, pressure sensors, and pyroelectric sensors.Also, the piezoelectric element according to an embodiment of theinvention may be applied to a ferroelectric element of a ferroelectricmemory device or the like.

What is claimed is:
 1. A piezoelectric element comprising: apiezoelectric layer comprising a complex oxide having a perovskitestructure with an A site and a B site; and electrodes provided to thepiezoelectric layer, wherein the complex oxide further contains a firstdopant element that is at least one selected from the group consistingof sodium, potassium, calcium, strontium and barium, and a second dopantelement that is cerium; wherein an A site contains bismuth, the firstdopant element and the second dopant element, and a B site containsiron; and wherein the A site has a defect, and the B site containsbismuth.
 2. The liquid ejecting head according to claim 1, wherein thecomplex oxide further contains barium titanate.
 3. A liquid ejectinghead comprising the piezoelectric element as set forth in claim
 1. 4. Aliquid ejecting apparatus comprising the liquid ejecting head as setforth in claim 3.